Defining Predation (+,-)



  • An organism (predator) that consumes all or part of another organism (prey)
    • benefits its own fitness
    • reduces the growth, fecundity and survival of the prey population


1. True predators:

2. Grazers:

3. Parasites:

Parasitoid Bodysnatchers: complicating predator definitions…


Predator behavior is super diverse


  • Behaviors to capture prey differ vastly
    • consumption rate:
    • consumption rate impacts populations


  • True predators and grazers are mostly foragers
    • searching (active foraging)
    • sit and wait (passive foraging)


  • Prey behavior (evasiveness) impacts consumption rate


  • Parasites rely on direct transmission
    • contact is density dependent

Optimal Foraging Theory




  • Obtaining food provides energy


  • Searching for and capturing food uses energy


  • Foraging is a banking problem: Return on Investment


  • To maximize fitness a forager must balance these

Optimal foraging should be related to density




  • Can predators be choosy?
    • Prey densities impact handling/search times


  • # of foragers relates to prey density
    • competition for available prey
    • group foraging? (Hintz & Lonzarich 2018)


  • Predators should choose to forage in a patch with the highest quality

Optimal foraging in African predators: Energy use



  • Calorie use by big predators
    • Cheetahs = 9,000 Kj
    • Wild dogs = 15,000 Kj
    • Lions = ?
    • Humans = 9000 Kj


  • Foraging Strategies
    • Laziness
    • Thievery
    • Group hunting
    • Seasonal prey choice

Optimal foraging in African predators: Prey choice

Consumption is an agent of natural selection: Defense

Defenses can be ‘constitutive’ of ‘induced’

Predators also adapt to prey (Cattau et al. 2017)

Predation can promote biodiversity




  • If they consume the strongest competitor then the community may become more ‘even’


  • Relieves competitive pressure on other species enabling coexistence


  • Predation structures communities

Predator vs Prey populations (Basics)

Prey populations are always lower in the presence of predators

Impacts of predation on populations is complex…


  • Behavior/adaptations of predators and prey
    • natural selection


  • Compensatory responses


  • Assumption of a 1 vs 1 relationship


  • Life histories via reproductive traits


  • Start Simple: Lynx vs Rabbit

Lotka Voltera: Modelling predator-prey dynamics


  • These predator-prey patterns are described in the Lotka-Voltera 2 species model
    • 2 basic components:
    • P = # of predators
    • N = # of prey


  1. Start with a lot of rabbits, who does well?
  2. Populations of lynx will ….
  3. Why does time matter at this step?
  4. Populations of prey will….
  5. Food for predators will….
  6. Over time predator populations will ….

Lotka-Voltera predicts coupled population cycles

Lotka Voltera equations


  • With no predators, prey populations (N) increase exponentially
    • dN/dt = rN
    • r = growth rate


  • Predators remove prey at some rate
    • dN/dt = rN - aPN
    • a = attacking efficiency



  • Prey stable when dN/dt = 0
  • In the absence of food, predator populations (P) will decline
    • dP/dt = -qP
    • q = mortality rate


  • Mortality buffered by births (faPN)
    • dP/dt = faPN -qP
    • food gain (aPN)
    • efficiency of food to offspring (f)


  • Predator stable when dP/dt = 0